1. Field of the Invention
This invention relates to a null-adjusting tool, and more particularly to a null-adjusting tool for the precise alignment of a tilt sensor to the vertical or the local gravity vector.
2. Description of the Prior Art
Leveling or tilt-sensing devices are well known in the art. A simple example is a carpenter's level containing an arc-shaped elongated sealed galss tube, partially filled with a liquid. An air bubble in the sealed tube responds to the position of the level giving a visual indication of the inclination from the vertical or from the horizontal. An improved bubble level, also known in the art and described in patent application Ser. No. 486,631 by Swartz, et al, filed Apr. 20th, 1983 and assigned to the assignee of the present invention utilizes an arcuate tube partially filled with an electrically conducting liquid. Electrical contacts within the tube are attached to an electronic readout device for a more accurate measurement of tilt than is possible by visual interpretation of the position of an air bubble within the tube.
In order to take full advantage of the high accuracy offered by electrolytic-type tilt sensing devices, it is necessary to precisely align the tilt-sensing device to the local gravity vector. Accurate alignment of bubble levels of the electrolytic type have previously required null-adjusting tools that are of instrument quality, generally, precision machined micrometer mechanisms. After alignment, such tools remain attached to the device and become part of the tilt-sensing mechanism. They are delicate to use and expensive to manufacture.
In U.S. Pat. No. 4,378,693, filed Feb. 11, 1981 and issued Apr. 5, 1983 to E. C. Ratcliffe, a deflection measuring system is described which provides an electrical circuit for electronically leveling the tilt sensor. However, this circuit employs a D.C. coupled differential amplifier, which is subject to errors due to drift and D.C. offset.
The present invention incorporates a mechanical null-adjusting mechanism and a digital readout device in one portable tool that does not require micrometer or custom fine thread adjustment mechanisms, is simple to operate, and may be removed after alignment of the tilt sensor. Thus, one null-adjustment tool which is the subject of the present invention may be used to align a multiplicity of tilt sensors such as might be found in a system used to monitor the movement of a structure such as a building or a bridge.